Electronic messaging systems of the related art come in various different forms, of which one particularly well known and widely used system is Internet e-mail. However, electronic messaging systems like Internet e-mail are inherently insecure and suffer from a large number of unwanted messages. As a result, many workers in this field have spent considerable effort developing mechanisms for filtering such unwanted messages. Most of these filtering mechanisms are based on intensive processing of messages to remove the unwanted messages, whilst allowing the wanted messages to proceed unhindered. In particular, these filtering mechanisms include anti-virus filtering mechanisms to automatically block messages containing viruses, worms, phishing attacks, spyware and Trojans as various forms of malicious message content. Further, anti-spam filtering mechanisms identify and block delivery of junk e-mail messages containing unsolicited advertising for products and services. Further still, content filtering mechanisms provide highly sophisticated lexical analysis of messages to automatically filter offensive terms in many different languages and also to identify messages which relate to certain words, terms and phrases where a filtering action is required in relation to privacy, confidentiality, a regulatory compliance requirement or other security concerns. It is often desirable to employ these differing technologies in combination to provide more effective multi-layered filtering. However, a problem arises in that these more complex filtering mechanisms and the combined use of multiple separate filtering mechanisms places heavy loads on the apparatus which perform these filtering functions. In many cases, these limitations of the hardware infrastructure are one of the main factors that inhibit growth of such electronic messaging systems.
In the related art, Internet email and SMTP (Simple Mail Transfer Protocol) are discussed in detail in RFC2821 of April 2001 (see www.rfc.net). SMTP runs over TCP/IP as discussed in detail in RFC793 of September 1981 and subsequent RFC publications.